Building block



FIG. 1 is a perspective view of a building block;

FIG. 2 is another perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a right side view thereof, and which is identical to left side view (not shown);

FIG. 5 is a top view thereof; and,

FIG. 6 is a perspective view of a building block being connected together with other building blocks.

The features shown in broken lines form no part of the claimed invention. 

CLAIM The ornamental design for a building block, as shown and described. 